1. Technical Field of the Invention
The present invention relates generally to an automotive obstacle recognition system equipped with a radar which is designed to emit a radar wave ahead of a vehicle and to receive a radar return to recognize an obstacle present in a frontal detection range.
2. Background Art
Automotive obstacle recognition systems are known in the art which are designed to emit radar waves such as light waves or milimetric waves over a given angular range and receive a return of the wave to recognize an object present ahead of the vehicle. As such systems, there have been proposed a collision alarm apparatus which measures the distance to an obstacle such as a preceding vehicle and outputs an alarm signal and a cruise control apparatus which controls the speed of the vehicle to keep the distance to a preceding vehicle.
Japanese Patent First Publication No. 11-38141 discloses an automotive obstacle recognition system. This system is designed to emit a sequence of radar pulses in a given scanning direction which is either of two directions: a horizontal direction (i.e., a width-wise direction of a vehicle) and a vertical direction without sweeping the pulse sequence in a reference direction that is the other of the horizontal and vertical directions and receive returns of the radar pulses from an object to determine the distance to and angular position of the object. After completion of processing of data sampled over one scanning line, the system shifts the scanning direction to the reference direction and emits a second sequence of radar pulses in the shifted scanning direction. This operation is repeated until completion of scanning of the whole of a detection range, thereby determining the distance to the object and two angular positions of the object in the vertical and horizontal directions. This is known as a three-dimensional recognition system.
The above automotive obstacle recognition system recognizes radar returns as dots and collects some of them over one scanning line which meet given conditions related to the location thereof and the interval therebetween in a width-wise direction of the system vehicle into one group as a presegment and also collects some of the presegments which meet a condition in which the interval between adjacent two of the presegments is shorter than a given distance in addition to the above conditions into one group as a main segment.
In order to save RAMs and decrease the operating time, the automotive obstacle recognition system does not handle all of the points recognized over one scanning line, but groups some of the points, which are arrayed across a central one along one scanning line and which meet the given conditions, together as the presegment. When the number of presegments reaches a given upper limit, the presegmenting operation is terminated. In practice, the system scans 105 points on one scanning line and analyzes the points alternately in the right and left directions from the 53th point that is a central one of the 105 points to produce the presegment.
For instance, when the system vehicle is running around a curve, the obstacle recognition system may detect a roadside obstacle near a central area of the radar detection range, while a preceding vehicle or target may be detected near an end of the radar detection range. In this case, since the presegmenting operation is, as described above, initiated from a central one of points recognized over one scanning line, the number of presegments may, as shown in FIG. 11, reach the upper limit before the target, as enclosed with a broken line, is recognized by the system. Specifically, the above obstacle recognition system encounters the problem in that a preceding vehicle is running on the same lane as the system vehicle, but it may not be tracked by the system.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an obstacle recognition system for automotive vehicles which is designed to recognize targets such as preceding vehicles to be tracked by a radar precisely with a decreased capacity of memory even when a system vehicle is turning a curve.
According to one aspect of the invention, there is provided an obstacle recognition apparatus for a vehicle which comprises: (a) a radar emitting radar waves to scan a given angular range in a width-wise direction of a vehicle equipped with the obstacle recognition apparatus, the radar receiving returns of the radar waves from objects present in the given angular range to determine distances to and angular directions of the objects in the width-wise direction of the vehicle; (b) a curve radius determining circuit determining a radius of a curve in a road on which the vehicle is traveling; and (c) an obstacle recognition circuit analyzing the returns of the radar waves received by the radar to recognize as targets a given number of the obstacles which are closer to a reference angular direction defined within the given angular range, the obstacle recognition circuit changing the reference angular direction based on the radius of the curve determined by the curve radius determining circuit.
In the preferred mode of the invention, the obstacle recognition circuit analyzes the returns of the radar waves to recognize the obstacles as points in a coordinate system and performs a grouping operation to collect some of the points which meet a first grouping condition into groups. The grouping operation is initiated from the reference angular direction to the width-wise direction of the vehicle.
The radar scans the given angular range along scanning lines which extend in the width-wise direction of the vehicle and arrayed at given intervals in a vertical direction of the vehicle within a given vertical angular range. The obstacle recognition circuit performs a second grouping operation to collect some of the points into the groups in each of the scanning lines and also some of the groups which meet a second grouping condition into second groups as expressing the obstacles.
The number of the groups formed in the grouping operation along the scanning lines defined in end portions of the given angular range in a height-wise direction of the vehicle is smaller than that along the scanning lines defined in a central portion of the given angular range in the height-wise direction of the vehicle.
The obstacle recognition circuit determines a change in the reference angular direction as a function of a shift in angular direction from a central angular direction in the given angular range based on the radius of the curve determined by the radius curve determining circuit.
According to the second aspect of the invention, there is provided an obstacle recognition apparatus for a vehicle which comprises: (a) a radar emitting radar waves to scan a given angular range in a width-wise direction of a vehicle equipped with the obstacle recognition apparatus, the radar receiving returns of the radar waves from objects present in the given angular range to determine distances to and angular directions of the objects in the width-wise direction of the vehicle; (b) a curve determining circuit determining whether a road on which the vehicle is traveling is curved or not; and (c) an obstacle recognition circuit analyzing the returns of the radar waves received by the radar to recognize as targets a given number of the obstacles which are closer to a reference angular direction defined within the given angular range, when it is determined by the curve determining circuit that the road is curved, the obstacle recognition circuit shifting the reference angular direction in an inward direction of the curved road.